1. Field of the Invention:
This invention relates to a color sign inserting circuit for a video signal reproducing system for inserting signs consisting of color characters or the like in the video reproduction by a video signal reproducing system such as a video disc player or a video tape recorder.
2. Description of the Prior Art:
In the prior art video signal reproducing systems, particularly in those for use in the home, signs consisting of characters or the like could be inserted only as monochrome signs as disclosed in, for instance, Japanese Laid-open Application No. 56-106477. This is so because in the prior art character sign insertion techniques a very complicated circuit is required if it is intended to obtain stable display of inserted signs in color. The complicated circuit leads to cost increase and is also liable to have adverse effects on other video signal processing circuits.
More particularly it is difficult to color-synchronize a color sign signal to the reproduced video signal with the phase precision necessary for the burst color signal. Therefore, the color hue of the inserted sign is liable to fluctuate. Secondly, the time axis of the color sign signal to be inserted in the reproduced video signal is liable to drift with fluctuations of the temperature or power supply voltage. Therefore, it is again difficult to stabilize the color hue. Thirdly, fluctuations of the characteristics of the component parts in the system and also functuations in the time axis compensation performance have adverse effects on the color hue of the display sign. To overcome this, a complicated circuit must be added, inevitably leading to cost increase.
The above difficulties have hindered the promotion of the display of inserted signs in color. Up to date, however, video signal reproducing systems are widely used, and there is strongly increasing demand for the realization of the display of inserted signs in color not only because this can elevate the commercial value of the systems, but also because this is a great factor for improving the operability of versatile systems from the standpoint of human engineering.